455 research outputs found
Millimeter- and Submillimeter-Wave Observations of the OMC-2/3 Region. II. Observational Evidence for Outflow-Triggered Star Formation in the OMC-2 FIR 3/4 Region
We have carried out the observations of the OMC-2 FIR 3/4 region with the NMA
and ASTE in the HCO (1--0), CO (3--2, 1--0), SiO (=0,
=2--1), CS (2--1), and CHOH (=7--6) lines and in the 3.3 mm
continuum emission. Our NMA observations in the HCO emission have
revealed 0.07 pc-scale dense gas associated with FIR 4. The CO
(3--2,1--0) emission shows high-velocity blue and red shifted components at the
both north-east and south-west of FIR 3, suggesting a molecular outflow nearly
along the plane of the sky driven by FIR 3. The SiO and the CHOH emission
are detected around the interface between the outflow and the dense gas.
Furthermore, the CO (1--0) emission shows an L-shaped structure in the
P-V diagram. These results imply presence of the shock due to the interaction
between the molecular outflow driven by FIR 3 and the dense gas associated with
FIR 4. Moreover, our high angular-resolution observations of FIR 4 in the 3.3
mm continuum emission have first found that FIR 4 consists of eleven dusty
cores. The separation among these cores is on the same order of the Jeans
length, suggesting that the fragmentation into these cores has been caused by
the gravitational instability. The time scale of the fragmentation is similar
to the time scale of the interaction between the molecular outflow and the
dense gas. We suggest that the interaction between the molecular outflow from
FIR 3 and the dense gas associated with FIR 4 triggered the fragmentation into
these dusty cores, and hence the next generation the cluster formation.Comment: 13 pages, 9 figures. Accepted by Ap
Millimeter- and Submillimeter-Wave Observations of the OMC-2/3 Region; I. Dispersing and Rotating Core around an Intermediate-mass Protostar MMS 7
We report the results of H13CO+(1-0), CO(1-0), and 3.3 mm dust continuum
observations toward one of the strongest mm-wave sources in OMC-3, MMS 7, with
the Nobeyama Millimeter Array (NMA) and the Nobeyama 45 m telescope. With the
NMA, we detected centrally-condensed 3.3 mm dust-continuum emission which
coincides with the MIR source and the free-free jet. Our combined H13CO+
observations have revealed a disk-like envelope. The size and the mass of the
disk-like envelope are 0.15 times 0.11 pc and 5.1 - 9.1 M_sun, respectively.
The combined map also shows that the outer portion of the disk-like envelope
has a fan-shaped structure which delineates the rim of the CO(1-0) outflow
observed with the NMA. The position-velocity (P-V) diagrams in the H13CO+ (1-0)
emission show that the velocity field in the disk-like envelope is composed of
a dispersing gas motion and a possible rigid-like rotation. The mass dispersing
rate is estimated to be (3.4 - 6.0) times 10^-5 M_sun/yr, which implies that
MMS 7 has an ability to disperse ~10 M_sun during the protostellar evolutional
time of a few times 10^5 yr. The specific angular momentum of the possible
rotation in the disk-like envelope is nearly two orders of magnitude larger
than that in low-mass cores. The turn-over point of the power law of the
angular momentum distribution in the disk-like envelope (< 0.007 pc), which is
likely to be related to the outer radius of the central mass accretion, is
similar to the size of the 3.3 mm dust condensation. The intermediate-mass
protostar MMS 7 is in the last stage of the main accretion phase and that the
substantial portion of the outer gas has already been dispersed, while the mass
accretion may still be on-going at the innermost region traced by the dusty
condensation.Comment: 19 pages, 9 figures, ApJ accepted pape
Arcsecond resolution images of the chemical structure of the low-mass protostar IRAS 16293-2422
It remains a key challenge to establish the molecular content of different
components of low-mass protostars, like their envelopes and disks, and how this
depends on the evolutionary stage and/or environment of the young stars.
Observations at submillimeter wavelengths provide a direct possibility to study
the chemical composition of low-mass protostars through transitions probing
temperatures up to a few hundred K in the gas surrounding these sources. This
paper presents a large molecular line survey of the deeply embedded
protostellar binary IRAS 16293-2422 from the Submillimeter Array (SMA) -
including images of individual lines down to approximately 1.5-3" (190-380 AU)
resolution. More than 500 individual transitions are identified related to 54
molecular species (including isotopologues) probing temperatures up to about
550 K. Strong chemical differences are found between the two components in the
protostellar system with a separation between, in particular, the sulfur- and
nitrogen-bearing species and oxygen-bearing complex organics. The action of
protostellar outflow on the ambient envelope material is seen in images of CO
and SiO and appear to influence a number of other species, including
(deuterated) water, HDO. The effects of cold gas-phase chemistry is directly
imaged through maps of CO, N2D+ and DCO+, showing enhancements of first DCO+
and subsequently N2D+ in the outer envelope where CO freezes-out on dust
grains.Comment: Accepted for publication in A&A, 30 pages, 22 figure
Cold Water Vapor in the Barnard 5 Molecular Cloud
After more than 30 yr of investigations, the nature of gas-grain interactions at low temperatures remains an unresolved issue in astrochemistry. Water ice is the dominant ice found in cold molecular clouds; however, there is only one region where cold ((is) approximately 10 K) water vapor has been detected-L1544. This study aims to shed light on ice desorption mechanisms under cold cloud conditions by expanding the sample. The clumpy distribution of methanol in dark clouds testifies to transient desorption processes at work-likely to also disrupt water ice mantles. Therefore, the Herschel HIFI instrument was used to search for cold water in a small sample of prominent methanol emission peaks. We report detections of the ground-state transition of o-H2O (J = 110-101) at 556.9360 GHz toward two positions in the cold molecular cloud, Barnard 5. The relative abundances of methanol and water gas support a desorption mechanism which disrupts the outer ice mantle layers, rather than causing complete mantle removal
Imaging Simulations of the Sunyaev-Zel'dovich Effect for ALMA
We present imaging simulations of the Sunyaev-Zel'dovich effect of galaxy
clusters for the Atacama Large Millimeter/submillimeter Array (ALMA) including
the Atacama Compact Array (ACA). In its most compact configuration at 90GHz,
ALMA will resolve the intracluster medium with an effective angular resolution
of 5 arcsec. It will provide a unique probe of shock fronts and relativistic
electrons produced during cluster mergers at high redshifts, that are hard to
spatially resolve by current and near-future X-ray detectors. Quality of image
reconstruction is poor with the 12m array alone but improved significantly by
adding ACA; expected sensitivity of the 12m array based on the thermal noise is
not valid for the Sunyaev-Zel'dovich effect mapping unless accompanied by an
ACA observation of at least equal duration. The observations above 100 GHz will
become excessively time-consuming owing to the narrower beam size and the
higher system temperature. On the other hand, significant improvement of the
observing efficiency is expected once Band 1 is implemented in the future.Comment: 16 pages, 12 figures. Accepted for publication in PASJ. Note added in
proof is include
The Sunyaev-Zel'dovich Effect at Five Arc-seconds: RXJ1347.5-1145 Imaged by ALMA
We present the first image of the thermal Sunyaev-Zel'dovich effect (SZE)
obtained by the Atacama Large Millimeter/submillimeter Array (ALMA). Combining
7-m and 12-m arrays in Band 3, we create an SZE map toward a galaxy cluster
RXJ1347.5-1145 with 5 arc-second resolution (corresponding to the physical size
of 20 kpc/h), the highest angular and physical spatial resolutions achieved to
date for imaging the SZE, while retaining extended signals out to 40
arc-seconds. The 1-sigma statistical sensitivity of the image is 0.017 mJy/beam
or 0.12 mK_CMB at the 5 arc-second full width at half maximum. The SZE image
shows a good agreement with an electron pressure map reconstructed
independently from the X-ray data and offers a new probe of the small-scale
structure of the intracluster medium. Our results demonstrate that ALMA is a
powerful instrument for imaging the SZE in compact galaxy clusters with
unprecedented angular resolution and sensitivity. As the first report on the
detection of the SZE by ALMA, we present detailed analysis procedures including
corrections for the missing flux, to provide guiding methods for analyzing and
interpreting future SZE images by ALMA.Comment: 20 pages, 13 figures. Accepted for publication in PAS
Millimeter- and Submillimeter-Wave Observations of the OMC-2/3 Region. III. An Extensive Survey for Molecular Outflows
Using the ASTE 10 m submillimeter telescope and the 1.4 m Infrared Survey
Facility (IRSF), we performed an extensive outflow survey in the Orion
Molecular Cloud -2 and -3 region. Our survey, which includes 41 potential
star-forming sites, has been newly compiled using multi-wavelength data based
on millimeter- and submillimeter-continuum observations as well as radio
continuum observations. From the CO (3-2) observations performed with the ASTE
10 m telescope, we detected 14 CO molecular outflows, seven of which were newly
identified. This higher detection rate, as compared to previous CO (1-0)
results in the same region, suggests that CO (3-2) may be a better outflow
tracer. Physical properties of these outflows and their possible driving
sources were derived. Derived parameters were compared with those of CO
outflows in low- and high-mass starforming regions. We show that the CO outflow
momentum correlates with the bolometric luminosity of the driving source and
with the envelope mass, regardless of the mass of the driving sources. In
addition to these CO outflows, seven sources having NIR features suggestive of
outflows were also identified.Comment: Accepted to Astrophysical Journal, high resolution images at
http://www.asiaa.sinica.edu.tw/~satoko_t/papers/ms.ST.pd
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